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About half the diamonds studied from the Cenozoic placer deposits along the Namibian coast belong to the peridotitic suite. The peridotitic mantle source is heterogeneous ranging from lherzolitic to strongly Ca depleted (down to 0.24 wt.% CaO in garnet) and shows large variations in Cr/Al ratio, illustrated by very low to very high Cr 2 O 3 contents in garnet (2.6-17.3 wt.%). The Cr-rich...
This paper outlines the development of a multi-disciplinary strategy to focus exploration for economic kimberlites on the Ekati property. High-resolution aeromagnetic data provide an over-arching spatial and magnetostratigraphic framework for exploration and kimberlite discovery at Ekati, and hence also for this investigation. The temporal, geomagnetic, spatial and related attributes of kimberlites...
The abundances of the mildly incompatible elements Al, Cr, V, Sc and Yb in more than 1700 mantle peridotite bulk rock analyses are interpreted in the light of a fractional melting model based on experimentally measured partition coefficients (D) and melting reaction stoichiometries. All peridotites examined, irrespective of sample type (abyssal peridotites, orogenic massifs, ophiolites, on/off craton...
Fifty diamond crystals of different morphological types (octahedra, dodecahedroids, cubes and single tetrahexahedroid) with differing internal structures were examined using methods of cathodoluminescence (CL), anomalous birefringence and local infrared (IR) analysis. The main objective of the study was to examine the regularities of nitrogen impurity distribution in diamond with differing internal...
Highly aluminous xenoliths include kyanite-, corundum- and coesite-bearing eclogites, grospydites and alkremites. These xenoliths are present in different kimberlites of Yakutia but have most often been found in Udachnaya and other pipes of the central Daldyn-Alakitsky region. Kimberlites of this field also contain eclogite-like xenoliths with kyanite and corundum that originate in the lower crust...
Peridotitic clinopyroxene (cpx) and pyrope garnet xenocrysts from four kimberlite pipes in the Kaavi-Kuopio area of Eastern Finland have been studied using major and trace element geochemistry to obtain information on the vertical compositional variability of the underlying mantle. The xenocryst data, when combined with the petrological constraints provided by peridotite xenoliths, yield a relatively...
Previously proposed methods of area selection for diamond-prospective regions have predominantly relied on till geochemistry, airborne geophysics, and/or an appraisal of tectonic setting. Herein we suggest that a novel, deep-probing geophysical technique-electromagnetic studies using the natural-source magnetotelluric (MT) method-can contribute to such an activity. Essentially, diamondiferous regions...
Silicate and oxide mineral inclusions in diamonds from the geologically and historically important De Beers Pool kimberlites in Kimberley, South Africa, are characterised by harzburgitic compositions (>90%), with lesser abundances from eclogitic and websteritic parageneses. The De Beers Pool diamonds contain unusually high numbers of inclusion intergrowths, with garnet+orthopyroxene+/-chromite+/-olivine...
Sixteen kimberlite boulders were collected from three sites on the Munro and Misema River Eskers in the Kirkland Lake kimberlite field and one site on the Sharp Lake esker in the Lake Timiskaming kimberlite field. The boulders were processed for heavy-mineral concentrates from which grains of Mg-ilmenite, chromite, garnet, clinopyroxene and olivine were picked, counted and analyzed by electron microprobe...
The tectonic setting of British Columbia (BC) differs from classic diamond-bearing intracratonic regions such as the Northwest Territories and South Africa. Nevertheless, several diamond occurrences have been reported in BC. It is also known that parts of the province are underlain by Proterozoic and possibly Archean basement. Because the continents of today are composites of fragments of ancient...
Modes and compositions of minerals in Slave mantle xenoliths, together with their pressures and temperatures of equilibrium were used to derive model depth profiles of P- and S-wave velocities (Vp, Vs) for composites equivalent to peridotite, pyroxenite and eclogite. The rocks were modeled as isotropic aggregates with uniform distribution of crystal orientations, based on single-crystal elastic moduli...
The position of the transition from spinel peridotite to garnet peridotite in a simplified chemical composition has been determined experimentally at high pressures and high temperatures. The univariant reaction MgCr 2 O 4 +2Mg 2 Si 2 O 6 =Mg 3 Cr 2 Si 3 O 12 +Mg 2 SiO 4 , has a negative slope in P-T space...
Mantle xenoliths and xenocrysts were retrieved from three of the 88-86 Ma Buffalo Hills kimberlites (K6, K11, K14) for a reconnaissance study of the subcontinental lithospheric mantle (SCLM) beneath the Buffalo Head Terrane (Alberta, Canada). The xenoliths include spinel lherzolites, one garnet spinel lherzolite, garnet harzburgites, one sheared garnet lherzolite and pyroxenites. Pyroxenitic and wehrlitic...
Experimental research on K-rich phases and observations from diamond inclusions, UHP metamorphic rocks, and xenoliths provide insights about the hosts for potassium at mantle conditions. K-rich clinopyroxene (Kcpx-KM 3+ Si 2 O 6 ) can be an important component in clinopyroxenes at P>4 GPa, dependent upon coexisting K-bearing phases (solid or liquid) but not, apparently,...
Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic. Unlike many lithospheric peridotites, the Sloan samples are also depleted in incompatible trace elements, as shown by the composition of separated...
Porphyroclastic enstatite in a garnet lherzolite xenolith from the Monastery Mine kimberlite, South Africa, has exsolved pyrope garnet, Cr-diopside and Al-chromite, and the specimen is interpreted as representing a transition from fertile harzburgite, (containing high Ca-Al-Cr enstatite) to granular garnet lherzolite. Although the exsolved phases occur in morphologically different forms (fine and...
The Quirico Basin covers an area of 10,000 km 2 and is situated to the west of the conventionally defined southwestern margin of the Archean Sao Francisco craton in Minas Gerais State, Brazil. The sedimentary infill of the Quirico Basin consists of lightly metamorphosed shallow marine clastic bedrock sediments of the Bambui Group (~650+/-15 Ma), unconformably overlain by Early Cretaceous terrigenous...
Eclogites from the Earth's mantle found in kimberlites provide important information on craton formation and ancient geodynamic processes because such eclogites are mostly Archean in age. They have equilibrated over a range of temperatures and pressures throughout the subcratonic mantle and some are diamond-bearing. Most mantle eclogites are bimineralic (omphacite and garnet) rarely with accessory...
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